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 he dying corals
of the Florida Keys could be an early warning of tough times
ahead for the planet's environment, Cornell University ecologists
worry. The reason: hundred-year-old corals are succumbing to
diseases they previously survived.
 Increasing global temperatures
and worsening pollution, the ecologists say, could place so much
stress on ecosystems that organisms of all kinds will face new
challenges.
"When we see corals that
have persisted for hundreds of years suddenly die from opportunistic
infections, we have to wonder what has changed in their environment,"
says C. Drew Harvell, associate professor of ecology at Cornell.
Harvell organized a session,
"Diseases of the Ocean: A New Environmental Challenge,"
at the annual January meeting of the American Association for
the Advancement of Science (AAAS) to bring together leading microbiologists,
ecologists and pathologists to evaluate the environmental threats
from disease in the ocean. Speaking in the session was Kiho Kim,
a postdoctoral research associate with Harvell at Cornell, who
reported on an unusual disease in Florida Keys corals.
Kim said that monitoring of
sea fan corals in the Keys, where up to 40 percent of sea fans
are infected by a fungal disease and many have already died,
suggests that lower water quality and higher ocean temperatures
stress corals and increase their susceptibility to disease. He
said the Florida findings support a growing consensus among scientists
worldwide that as ocean ecosystems become degraded they will
offer more favorable places for disease outbreaks and the emergence
of new pathogens.
"We didn't begin our
study of sea fans to monitor death and destruction," Harvell
said. "Originally, we were interested in the natural disease-resistance
properties of corals, such as the antibacterial and antifungal
chemicals they produce, because some of those compounds may be
useful in human medicine. That disease resistance normally keeps
a coral alive for hundreds of years, despite living in an ocean
full of potential pathogens."
She said Garrett Smith of
the University of South Carolina at Aiken was responsible for
tracing the sea fan disease to a common, soil-dwelling fungus.
A type of Aspergillus fungus, washed out to sea by land
erosion, collects on the flexible, fan-shaped surface of the
corals and promotes an aspergillosis infection that first discolors
and eventually causes lesions and tumors as it destroys some
corals, the researchers said. Sea fans, which position themselves
perpendicular to water currents are especially vulnerable to
any pathogenic organisms in the passing water, Harvell noted.
"Somehow, a soil pathogen
that was best known for infecting aged and immune-compromised
humans has crossed the land-sea barrier," Harvell said.
"Now, one of our jobs is to discover what has compromised
the resistance of the corals at some sites. Although a significant
number of sea fans have died at a few sites, at many locales
they recover from infections, pointing to the success of their
natural resistance."
While coral disease is reported
throughout the Caribbean, the reef ecosystems of the Florida
Keys may be particularly vulnerable because they are close to
what ecologists call "natural stressors," such as fluctuating
water temperatures and substantial freshwater runoff, Harvell
said. The situation has worsened in recent years, the Cornell
ecologist observed, with multiple "anthropogenic stressors,"
such as eutrophication, siltation and other effects of intensive
human use of the land and offshore waters.
"Then you have rising
water temperatures of the oceans," Harvell added. "Whether
you believe that global warming is a function of human activity
and whether last year's El Niño was a symptom of global
warming, the fact is that sea temperatures globally in 1998 were
high. And 1998 was the worst year ever recorded globally for
coral bleaching."
Corals bleach (or lose their
symbiotic algae) when stressed by high temperatures, Harvell
explained, adding: "I think we have to question the relationship
between temperature stresses and diseases of the oceans."
Lately in the Florida Keys,
coral death has been occurring so suddenly and rapidly that Harvell
and Kim must monitor their research sites three times a year.
She credits the assistance of Cornell undergraduate researchers,
including Alisa Alker, who dive from NOAA vessels and return
to the laboratory to perform biological assays of coral samples.
"With a very few exceptions,
we know so little about the pathogenic organisms that are affecting
the coral reefs," Harvell said. "We don't know if new
diseases are emerging, if the hosts are becoming more susceptible
or both. We need to identify these new diseases and we should
do it now while we have the chance. Disease ecology is poorly
understood in the ocean because diseases are like lightning strikes
they hit unexpectedly, burn through a population, and then they
are often gone."
Harvell and Kim conduct their
studies from the Keys Marine Laboratory in Long Key, with the
assistance of Reef Relief in Key West. Their research is supported
by the National Science Foundation, National Oceanic and Atmospheric
Administration (NOAA) and the New England Bio Labs Foundation.
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cornell.edu.